74 THE CONSTITUTION OF THE SILICATES. [bull. 125. 
Several other hydrous silicates of magnesium seem to belong in this 
group, but their nature is altogether doubtful. Thus we have 
Aphrodite Mg 2 H 4 (Si0 4 ) 2 
Kerolite Mg(Si0 4 ) 2 H 5 (MgOH) 
Deweylite is possibly 
/Si0 4 =H, 
Mg< 
>Si0 4 =(MgOH) 2 + 2H 2 
Mg< 
\SiO~H 3 
and genthite is similar, with part of the magnesium replaced by nickel. 
Sepiolite may be a trisilicate, with the formula H 2 =Si 3 8 = (MgOH) 2 , in 
which case conarite is the corresponding nickel salt. These symbols 
are to be regarded as suggestions only. Two other trisilicates — eudidy- 
mite and epididymite — should also be noted at this point. The two 
species have the same empirical formula, HNaGrlSi 3 8 , which, doubled, 
becomes 
Na 2 
/Si 3 8x 
Gl< >G1 
X Si 3 0/ 
II 
H 2 
a structure conformable to the type of the orthosilicates already con- 
sidered. The isomerism between eudidymite and epididymite is 
explainable by giving one species the constitution just written, while 
the other, in place of Ka 2 and H 2 , would have the two groups NaH. 
It can also be ascribed to a different linking with the oxygen of the 
acid, and the empirical formula HNaGlSi 3 8 can be put in two forms, 
thus : 
0=Si— O— Na o=Si— O 
o 
Si< >G1 and Si; 
r 
I x O— Na 
0=Si— O— H o=Si— O— H 
a third isomer being also conceivable. The doubled formula, however, 
brings out analogies with bertrandite and other species and there- 
fore, in default of evidence, is to be preferred. 
